virt:Fix a hidden bug in virt_filesystems

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
virt:Add a function to get primary disk filesystem type

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
virt-libguestfs:Add a parameter for different filesystem type guest

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
Merge pull request #1135 from liyangfnst/virt_sysprep_fs

virt-libguestfs: add differert filesystem test for virt-sysprep and fix some typoes